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''Xenorhabdus'' is a genus of motile, gram-negative bacteria from the family of the Enterobacteriaceae. It has the particularity that all the species of the genus live in symbiosis with soil entomopathogenic nematodes from the genus ''Steinernema''. Although no free-living forms of Xenorhabdus have ever been isolated outside of the nematode host, the benefits for the bacteria are still unknown. However, it has been demonstrated that the nematode can't establish within his insect host without the bacteria. The tripartite Xenorhabdus-nematode-insect interaction represents a model system in which both mutualistic and pathogenic processes can be studied in a single bacterial species. In laboratory, some species are virulent directly injected within the insect host, whereas others species need the nematode to penetrate into the insect. ==Lifecycle== 1. In the non-infestant-stage nematode living in the soil, ''Xenorhabdus'' spp. are carried in a specialized region of the intestine, termed the receptacle. 2. At the third-stage of development, the infective juvenile (IJs) invade the hemocoel of susceptible insect hosts. 3. The bacteria are released in the insect hemocoel, where they overcome the insect's defense systems and produce numerous virulence factors such as hemolysin and cytotoxin. They participate in suppressing insect immunity and killing the host. 4. The bacteria proliferate to high levels in the insect cadaver and produce diverse antimicrobial compounds that suppress the growth of antagonistic microorganisms. ''Xenorhabdus spp''. also secrete an array of exoenzymes that stimulate macromolecular degradation, the products of which, together with the bacteria themselves, are thought to provide a nutrient base for nematode growth and reproduction. 5. When nematode numbers become high and nutrients become limiting in the insect cadaver, nematode progeny re-associate with bacteria and differentiate into colonized, non-feeding IJs that emerge into the soil to forage for new hosts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Xenorhabdus」の詳細全文を読む スポンサード リンク
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